1. Field of the Invention
The present invention relates to an ophthalmologic apparatus and an ophthalmologic method for measuring information on an eye to be inspected, such as eye refractive power of the eye to be inspected.
2. Description of the Related Art
Conventionally, in an ophthalmologic apparatus for measuring eye refractive power or the like of an eye to be inspected, there is known a method of observing a transillumination image as a measure against occurrence of a measurement error. Here, the transillumination image is an image obtained by observing a pupil area illuminated from inside of the eye to be inspected by reflection light of transillumination observation light projected to a fundus of the eye to be inspected. When a crystalline lens as a transparent body has opacity due to cataract or the like, the opacified portion is observed as a dark shadow. Therefore, observation of the transillumination image is used for investigating the cause of the measurement error or the like.
Japanese Patent No. 3,244,873 discloses an ophthalmologic apparatus that can perform the transillumination observation using a measurement light source without an additional light source for the transillumination observation. When a measurement error occurs, the mode is changed to a transillumination observation mode, in which alignment is manually performed so as to avoid the opacity in the crystalline lens. Then, the eye refractive power is measured again while performing the transillumination observation.
Japanese Patent No. 4,469,205 discloses an ophthalmologic apparatus in which an automatic alignment reference position is changed based on a transillumination still image picked up in advance, and the alignment is performed while avoiding the opacified portion in the crystalline lens due to cataract or the like. Usually, an alignment target position of a measuring portion with respect to the eye to be inspected is set to be matched with the pupil center. However, when the crystalline lens has opacity so that a ring image necessary for measuring ocular refraction is partially lost, the measurement cannot be performed in a normal alignment position. Therefore, in the invention disclosed in Japanese Patent No. 4,469,205, when a measurement error occurs, the measurement error is to be reduced by moving the alignment target position so that the ring image for measurement avoids the opacified portion while viewing the transillumination still image picked up in advance. After a new alignment position is determined, a measurement screen is displayed again so that the measurement is restarted.
In addition, in a conventional ophthalmologic apparatus for measuring the eye refractive power of the eye to be inspected, it is known to display a transillumination image after measuring the eye refractive power value as a countermeasure when the eye refractive power measurement is not correctly performed due to a disease such as cataract. In the invention disclosed in Japanese Patent No. 4,469,205, alignment is first performed based on a corneal reflex image, and light from a light source for transillumination observation is projected to the fundus so that an image is picked up and stored as a still image during preliminary measurement or fogging operation. Then, when a refractive power measurement error occurs, the transillumination image as a stored still image is displayed in an enlarged manner.
In addition, in the conventional ophthalmologic apparatus, before an acquiring portion acquires specific information of the eye to be inspected, such as eye refractive power, a fundus image, or fundus blood flow, alignment (positional adjustment) of the acquiring portion with respect to the eye to be inspected is performed. As to the alignment, there is known an apparatus which automatically performs the alignment of the acquiring portion with respect to the eye to be inspected, by projecting an alignment index light beam to the cornea of the eye to be inspected, detecting a reflection image of the cornea of the eye to be inspected in a photoelectric manner, and driving the acquiring portion in three axis directions based on the detected information.
Further, there is known an apparatus which performs alignment (positional adjustment) involving the pupil of the eye to be inspected in consideration of the fact that most human eyes to be inspected have the corneal apex decentered from the pupil center, although depending on individual differences or pathologic factors. Japanese Patent No. 4,481,420 proposes an apparatus which detects a pupil position by utilizing the fact that the pupil portion is darker than other portions, and performs the alignment with the pupil center position when there is a difference between the alignment position based on an index image by cornea reflection and the pupil center position.
However, as to the ophthalmologic apparatus as described in Japanese Patent No. 3,244,873, it is necessary to manually perform the alignment during observation of the transillumination image. Therefore, it is difficult to maintain a positional relationship with the eye to be inspected while performing the measurement, and the operation becomes difficult. The ophthalmologic apparatus described in Japanese Patent No. 4,469,205 performs the change of the alignment position when measuring an ocular refractive index based on information of the transillumination still image. Therefore, there is a problem that desired alignment accuracy cannot be obtained when a fixation position of the eye to be inspected is different between when the ocular refractive index is measured and when the transillumination image is acquired. In addition, there is a problem that the measurement time is increased because the transillumination image is retrieved for correcting the alignment position every time a measurement error occurs. Further, there is a problem that the transillumination observation at a time point when the refractive power measurement error occurs cannot be performed, because the transillumination image is displayed as a still image without synchronization with occurrence of the refractive power measurement error.
In addition, the ophthalmologic apparatus as described in Japanese Patent No. 4,481,420, in which a dark portion is recognized as a pupil, has a problem that the pupil area is erroneously determined when lashes or the like overlap the pupil as a dark portion, and hence desired alignment accuracy cannot be obtained.